In packet communication using a high-speed access network such as two-way CATV or ADSL (Asymmetric Digital Subscriber Loop), it is a general practice to contract one or both of the minimum guaranteed rate and maximum limiting rate of packet transfer between a subscriber and the carrier, and decide a connection fee in accordance with the contracted value.
Although one contract is made for each subscriber in some cases, a plurality of contracts are sometimes made in accordance with services such as data, audio, and video services which a subscriber uses. Especially when a carrier applies different charging systems to different services, the minimum guaranteed rate and maximum limiting rate of packet transfer are contracted for each service which a subscriber uses, as in the latter case.
Also, depending on the type of service, the allowance of burst, maximum transfer delay time, and the like are also contracted in addition to the minimum guaranteed rate and maximum limiting rate of packet transfer.
To fulfil the contents of these contracts with subscribers, therefore, a packet transfer apparatus of the carrier of a packet network requires a packet transfer rate monitoring control apparatus.
This packet transfer rate monitoring control apparatus identifies an upper layer flow from the header information of a packet to be transferred, and compares, for each flow, the packet transfer rate with the minimum guaranteed rate or maximum limiting rate contracted by a subscriber in advance. In accordance with the comparison result or a service to which the flow belongs, the apparatus performs traffic priority control, polishing, shaping, and the like.
As the conventional packet transfer rate monitoring control apparatus, a UPC (Usage Parameter Control) apparatus in an ATM (Asynchronous Transfer Mode) network is known. For example, those described in U.S. Pat. Nos. 5,311,513 and 6,064,651 and Japanese Patent Laid-Open Nos. 9-46344 and 9-149046 are known.
Unfortunately, these conventional packet transfer rate monitoring control apparatuses define a contracted value of the maximum limiting rate by several types of parameters, and, if this contracted value is violated, discard the packet or lower the priority of transfer by adding a tag indicating the contract violation to the packet header, so that the contracted value of the maximum limiting rate is not exceeded for all flows.
This system works if the maximum limiting rate and minimum guaranteed rate are equal. However, if these values are different and the total of the maximum limiting rates of individual flows is set to exceed the interface rate of the packet transfer apparatus, and if traffic increases temporarily, the minimum guaranteed rates of some flows are no longer ensured although each individual flow does not exceed the maximum limiting rate.